Jun decides to help Shiena with her studies, which drives Naori crazy. Rumi, on the other hand, seems unusually indifferent about it. However, for Naori, it's clear that she needs to keep an eye on them. So, she quickly invites herself along.
What makes you say that? 
You'd better have a good reason!
ما الذي يجعلك تقولين هذا؟
!يستحسن أنّك تملكين سببًا جيدًا
Woher willst du das wissen?!
¿Por qué estás tan convencida?
Alguna razón tendrás.
¿Por qué estás tan convencida?
Alguna razón tendrás.
Comment tu peux en être sûre ?
Je veux une explication fiable.
Cosa te lo fa credere?
Pretendo una buona ragione!
Como você sabe?!
É bom ter um bom motivo!